This proposal is aimed at studying the long-term culture of human and rat functional pituitary tumor cells and somatic cell hybrids secreting growth hormone or prolactin. Hormone modulation by thyrotropin-releasing hormone (TRH), growth hormone releasing factor (GRF), thyroid hormones and other neurotransmitters will be studied. The human pituitary cell cultures will provide an in vitro model for studying mechanisms of hormone synthesis and release and provide further insights into the regulation of human prolactin and growth hormone secretion, the pathophysiology of pituitary tumors and female and male reproductive control and infertility.